Recently, an RFID tag is used in various scenes such as a distribution management system, a user authentication system, an electronic money system, or a transportation system. The RFID tag houses a small-sized integrated circuit (IC) chip together with an antenna in its housing having a card shape or the like, and is for reading and writing information from and in a reader/writer through radio waves without contact. Technologies related with the RFID tag are described, for example, in Japanese Laid-open Patent Publication No. 05-67254, Japanese Laid-open Patent Publication No. 08-69513, and Japanese Laid-open Patent Publication No. 2005-351877.
There is an RFID tag called a passive tag that does not include a built-in battery, and uses radio waves sent from a reader/writer as an electricity source of an IC chip. The passive tag can be operated semipermanently, and thus is used in various systems.
However, the conventional passive tag has a problem that the distance within which the passive tag can communicate with a reader/writer is short. Specifically, because the conventional passive tag generates operating electricity based on radio waves received from a reader/writer, the passive tag cannot be operated unless it is within a range that the passive tag can receive radio waves with the electricity necessary in generating operating electricity. In other words, the conventional passive tag can be operated only near a reader/writer because the passive tag needs to receive radio waves with sufficiently large electricity.